A system and method are disclosed for generating a gating signal for Positron Emission Tomographic (PET) data. Specifically, the system and method are related to generating a data driven gating signal for PET data acquired from multiple bed positions.
Medical imaging systems use non-invasive techniques to image and visualize internal structures and/or functional behavior of organs of a patient. Medical imaging systems are based on ultrasound, computed tomography (CT), x-ray, positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetic resonance (MR) techniques.
PET images from a patient are acquired over a time interval of several minutes for diagnosis, radiation therapy (RT) and radiation therapy planning (RTP). During the acquisition, patient movements due to respiration activity, cardiac activity and other gross patient movements results in noise signals. The noise signals generate blurring of the generated images, consequently resulting in wrong diagnosis and therapeutic decisions.
Conventionally, gating techniques are employed to mitigate the effects of respiration and cardiac motion on the PET data. A respiratory or cardiac motion signal acquired during the acquisition of the PET data, is used to identify portions of the PET data having similar phase of the quasi-periodic patient movements. Identified portions of PET data are used to determine motion free PET data. However, gated signals suffer from a low signal-to-noise ratio due to reduced photon counts recorded within a corresponding acquisition time interval. Image registration required for reducing the effects of motion data, use of independently acquired respiratory or cardiac data limit the quality of the gating signal generated through this technique.
Data driven gating is a class of techniques used to determine the respiratory and/or cardiac motion based on the acquired PET dataset. The acquired data is analyzed and a gating signal is generated for identifying data in a plurality of (for instance respiratory) motion states. Some data driven methods however generate a signal that is of arbitrary scale and sign. This can be problematic in certain applications where it is necessary to distinguish between e.g. inspiration and expiration, or diastole and systole. This is also the case for PET data acquired from multiple bed positions as this introduces the additional requirement of stitching the gating signal across the bed positions.
It is therefore desirable to develop a system and method for generating a gating signal from PET data with a fixed sign, especially for data acquired from multiple bed positions.